<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:controls="clr-namespace:Apex.Controls"
    xmlns:converters="clr-namespace:Apex.Converters">
    
    <Style TargetType="{x:Type controls:SelectableItemsControlItem}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type controls:SelectableItemsControlItem}">
                    <Grid>
                        <ContentPresenter />
                        <TextBlock>Test</TextBlock>
                    </Grid>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
    
</ResourceDictionary>